vgaoem.fon should be in two places on your hard drive C:\winnt\fonts and C:\winnt\system32\dllcache\
you can start xp from the setup disk and choose repair options\repair console
do a dir list on each of these folders to see if the file is there. If it's missing in one place you can copy it to the other. If it's in both places then rename one of them and copy the other their. If you still have the problem, then reverse the process by renaming the one you renamed back, and then copy it to the other folder. If still no go, you can expand the file off of the intstallation cd to both locations.
If you don't like that option, you could do a repair install from the setup disk, but you'll have to reinstall all the service packs.